Back in the middle of 2014, the stock market was rising through the roof. But the number-crunchers at the Bureau of Economic Analysis said the economy was shrinking, at a rate of 2.1 percent. Six months later, it's 2015. The BEA says the economy is growing at a rate of 5 percent. But the stock market is tumbling. Why is there so much difference between the stock market and the economy? Here's a short explainer.